Without limiting the scope of the present invention, its background is described with reference to constructing a subterranean well, as an example.
In conventional practice, the drilling of an oil or gas well involves creating a wellbore that traverses numerous subterranean formations. For a variety reasons, each of the formations through which the well passes is preferably sealed. For example, it is important to avoid an undesirable passage of formation fluids, gases or materials from the formations into the wellbore or for wellbore fluids to enter the formations. In addition, it is commonly desired to isolate producing formations from one another and from nonproducing formations.
Accordingly, conventional well architecture typically includes the installation of casing within the wellbore. In addition to providing the sealing function, the casing also provides wellbore stability to counteract the geomechanics of the formation such as compaction forces, seismic forces and tectonic forces, thereby preventing the collapse of the wellbore wall. The casing is generally fixed within the wellbore by a cement layer that fills the annulus between the outer surface of the casing and the wall of the wellbore. For example, once a casing string is located in its desired position in the well, a cement slurry is pumped via the interior of the casing, around the lower end of the casing and upward into the annulus. After the annulus around the casing is sufficiently filled with the cement slurry, the cement slurry is allowed to harden, thereby supporting the casing and forming a substantially impermeable barrier.
In standard practice, the wellbore is drilled in intervals with casing installed in each interval before the next interval is drilled. As such, each succeeding casing string placed in the wellbore typically has an outside diameter having a reduced size when compared to the previously installed casing string. Specifically, a casing to be installed in a lower wellbore interval must be passed through the previously installed casing strings in the upper wellbore intervals. In one approach, each casing string extends downhole from the surface such that only a lower section of each casing string is adjacent to the wellbore wall. Alternatively, the wellbore casing strings may include one or more liner strings, which do not extend to the surface of the wellbore, but instead typically extend from near the bottom end of a previously installed casing downward into the uncased portion of the wellbore. In such installations, the liner string may be set or suspended from a liner hanger positioned near the uphole end of the liner string.